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 * Copyright (c) 2014, Oracle America, Inc.

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 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"

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package org.openjdk.jmh.samples;


import org.openjdk.jmh.annotations.Benchmark;

import org.openjdk.jmh.annotations.BenchmarkMode;

import org.openjdk.jmh.annotations.Fork;

import org.openjdk.jmh.annotations.Mode;

import org.openjdk.jmh.annotations.OutputTimeUnit;

import org.openjdk.jmh.annotations.Scope;

import org.openjdk.jmh.annotations.Setup;

import org.openjdk.jmh.annotations.State;

import org.openjdk.jmh.runner.Runner;

import org.openjdk.jmh.runner.RunnerException;

import org.openjdk.jmh.runner.options.Options;

import org.openjdk.jmh.runner.options.OptionsBuilder;


import java.util.concurrent.TimeUnit;


@State(Scope.Thread)

@BenchmarkMode(Mode.AverageTime)

@OutputTimeUnit(TimeUnit.MILLISECONDS)

public class JMHSample_13_RunToRun {


 /*

  * Forking also allows to estimate run-to-run variance.

  *

  * JVMs are complex systems, and the non-determinism is inherent for them.

  * This requires us to always account the run-to-run variance as the one

  * of the effects in our experiments.

  *

  * Luckily, forking aggregates the results across several JVM launches.

  */


 /*

  * In order to introduce readily measurable run-to-run variance, we build

  * the workload which performance differs from run to run. Note that many workloads

  * will have the similar behavior, but we do that artificially to make a point.

  */


 @State(Scope.Thread)

 public static class SleepyState {

  public long sleepTime;


  @Setup

  public void setup() {

   sleepTime = (long) (Math.random() * 1000);

  }

 }


 /*

  * Now, we will run this different number of times.

  */


 @Benchmark

 @Fork(1)

 public void baseline(SleepyState s) throws InterruptedException {

  TimeUnit.MILLISECONDS.sleep(s.sleepTime);

 }


 @Benchmark

 @Fork(5)

 public void fork_1(SleepyState s) throws InterruptedException {

  TimeUnit.MILLISECONDS.sleep(s.sleepTime);

 }


 @Benchmark

 @Fork(20)

 public void fork_2(SleepyState s) throws InterruptedException {

  TimeUnit.MILLISECONDS.sleep(s.sleepTime);

 }


 /*

  * ============================== HOW TO RUN THIS TEST: ====================================

  *

  * Note the baseline is random within [0..1000] msec; and both forked runs

  * are estimating the average 500 msec with some confidence.

  *

  * You can run this test:

  *

  * a) Via the command line:

  *    $ mvn clean install

  *    $ java -jar target/benchmarks.jar JMHSample_13 -wi 0 -i 3

  *    (we requested no warmup, 3 measurement iterations; there are also other options, see -h)

  *

  * b) Via the Java API:

  *    (see the JMH homepage for possible caveats when running from IDE:

  *      http://openjdk.java.net/projects/code-tools/jmh/)

  */


 public static void main(String[] args) throws RunnerException {

  Options opt = new OptionsBuilder()

          .include(JMHSample_13_RunToRun.class.getSimpleName())

          .warmupIterations(0)

          .measurementIterations(3)

          .build();


  new Runner(opt).run();

 }
// 由于JVM的复杂性，每次测试结果都有差异，可以使用 @Fork 注解启动多个 JVM 经过多次测试来消除这种差异。

}